Telephone system



F. M. SLOUGH.

TELEPHONE SYSTEM.

APPLICATION FILED OCT-14,1914. RENEWED. MAY 25,192]. 1,407,892.

Patented Feb. 28, 1922.

2 SHEETS-SHEET h VB 1 OR.

WITNESSES:

BY W

F. M. SLOUGH.

TELEPHONE SYSTEM.

' APPLICATION FILED OCT-14,1914. RENEWED MAY 25,192.!

1,407,892. Patentd Feb. 28, 1922.

2 SHEETS-SHEET 2.

IN ENTO-R.

a I I' 7 WITNESSE j ATTORNEY UNITED STATES PATENT oFFIoE.

FRANK M. sLoUei oF ELYRIA, OHIO, ASSIGNOR, BY MESNE Assrcnnn:am's, TO STROMBERQGAR-LSON TELEPHONE MFG. 00., or noonnsrnn, NEW YORK, A

CORPORATION OF NEW YORK.

Specification of Letters Patent. Patentd Feb, 28, 1922.

Application filed October 14, 1914, Serial No. 866,583. iienewe'a m 25, 1921'. Serial No. 472,557.

To allevltom it may concern."

Be it known that I, FRANK M. SLoUoH,

a citizen of the United States, l'esldln at V l llyria, in the county of Lorain and S tate of Ohio, have invented certainnew and use- 'ful Improvements in Telephone Systems;

and I do hereby declare the following to be a full, clear,.and exact description oi the invention, such 1s will enable others skilled in the art to which it. appertains to make and use the same.

invention relates to telephone. systems, and more particularly to systems inwhich an associate multiple isemployed-that is, an improved system .in which the call of a subscriber is indicated at a plurality. of positions or before a plurality ofoperators,

and may be answered by any operator, one oi? the objects of my invention being to provide means to indicate to operators who answer a call the ,iact that it has already been answered, when that is the fact. I aim to indicate this in a suitable and ade-. quate manner, and to combine this feature with other-desirable features in such a way,

as-to enable the apparatus to be installed without prohibitive complications or expense.

Another object of my invention is to pre rent the operator from being connected to a line whose incoming call has already been answered by another operator. I aim to do this in a convenient and eflicient way and by such a combination of apparatus as to meet all operating conditions, such as lines of various resistance, capacity, etc.

Other objects of my invention and the invention itself will probably be better understood from a description of embodiments of my invention.

In Fig. l I have illustrated connecting links showing one embodiment of my invention.

Fig. 2 illustrates a second embodiment of my invention.

Fig. 3 illustrates a third embodiment of my invention.

Fig 4 illustrates a fourth embodiment-of F 5 illustrates in detail arelay emillustrated in Fig. 3.

I Referring first to the embodiment illustratedin Fig, 1, at I is illustrated a telephone line, here known as the calling line and which leads from a substation A to a main station at III. At II is shown a secend telephone line, which leads from a plu-v rality of substations, B, B B and B, to

in the form of a cord circuit C. Suitable switching means are provided for connecting the link conductors to the telephone lines, here shown as a ack J connected with the conductors 4 and 5 of the lineI and a plug,

P connected to what is known as the answerih'g end of thecord circuit. The switching meansi or connecting the cord to the line II consists of a. jackJ, connected to the line conductors 6 and 70f the line II and a plug. P in the calling end of the cord circuit.

Multiple jacks of the lines are shown at J and J The cord circuit of F ig. 2 is shown at C and terminates in plugs P and P The jacks J and J are connected by multiple conductors 8, 9 and 10 and the jacks'J 1 and J,

are connected by multiple conductors .11 and 12. The line I is provided with suitable line signaling apparatus shown as a line relay I), a line lamp E and with cut-oil mechanism including the cutoff relay F.

The line II. is provided with line signal apparatus including theline relay 1),, line lamp E and with cut-ofi 'mechanism including the cut-off relay F An operators set is provided at station III adapted to be connected to the cord circuit C, illustrated at Gr, and another operators set adapted to be connected atthe cord circuit 0,, shown at G,. The cord circuits C and C are at different positions and employed by difierent operators.

When the'plug-P is inserted into the jack (I, the relays F and H will be operated over a circuit including a resistance K, provided.

no other cord is connected to a multiple jack of the line I.- If, however, a cord such as the cord 0, is connected to a multiple, jack of the line I, the relay H thereof will have been operated and a shunt 131 will have been ed to the line or not, and a circuit will be completed through a relay M which will cause the illumination of a lamp N, and signal the operator to indicate to her that the call has already been answered. The operation of the relay L will also complete a circuit from a special tone device 0 through the operators set G, also indicating to her that the call has already been answered. If

the cord G is the first to be connected to the line I, the relay H will be operated, the shunt 13 completed, the operators set G will be connected to the cord and the operator will learn what station is desired. The plug P,

will then be inserted into the jack J, and the relay Q operated to disconnect the operator from the cord. The operator will then depress the ringing key E and the master key S,both of which will lock down. The ringing relay T will be operated, interrupting the cord, connecting on the ringing generator U and completing an alternate circuit for the relay Q.

lays'V and W will be operated, interrupting the ringing, completing thecord and restoring the original circuit of the relay Q.

, When the conversation is completed, the relay X will be operated, disconnecting the plug P from the cord, interrupting the circuit of the relay H and causing the operation of the signal Y, which indicates to the operator that the conversation is completed.

Perhaps my system and its functions will' be better understood from a detailed description' of the operation, which is as follows: Assuming first that the subscriber at A desires to communicate with the subscriber at B, the receiver 14 is removed from the switch book 15, which being spring pressed upward, will rise and engage the contact'l6, completing a circuit through the relay D, as follows: ground at 17--battery Zrelay D switch 1819 conductor 4 receiver 14-.-transmitter 20-c0ntacts 1615-conductor 5-contacts 2122 to ground at 23.

The relay D will be energized, attracting its armature 24 and closing a switch 2425,

completing a circuit through the line lamp E, as follows! 26resistance coil 27,E+

28v-24t--25Zl7. The same arrangement of line signal and lamp will beprovided at various positions, and the first operator available will insert a plug into the ack.

Assuming the operator controlling the cord C is the first to observe the call, the

The ringing will take place 1 until the subscriber responds, when the re-" of the jack J plug P of the cord C is inserted into the jack "J, the tip contact 30, sleeve contact 31 and ring contact 32, engaging respectively with the tip spring 33, sleeve spring 34 and thimble 35 of the jack. A circuitgwill be completed through the relays F and H as follows; ground at-34, relayF-contacts 35 and 32-switch 36-37-conductor 38-relayH resistance K-battery Z and ground 39. If no other cord has been connected to the line, the current flowing through this circuitwill be sutficient to operate the relays F and H; The relay F will attract its armatures 19 and 21, cutting off the line relay D and line lamp E from the line at 21-22 and 18-19, the relay H will attract its armature 40 closing a switch 40-41 in a shunt 13 about the'resi'stance device K, thereby, "as

will be explained, preventing any other operator from coming in to answer the call. The relay H will; also attract its armatures 4-2 and 43, opening a switch 43- 44: and closing switches 4345 and 4 246. The closing of the last two switches will connect the op erators set at G to the cord circuit through the conductors 47-418, the switches named,

switches 4c95() and 51-52 and conductors :73--54;. The operator now communicates with the subscriber'at A, learning that it is the subscriber at B that is desired. The line I? is tested in the usual manner, and having been found idle, which we will assume, the plug P, is inserted into the jack J the tip tact 62 engaging respectively" with the tip spring 63, sleeve spring 64 and thimble 65 When the connection was made with the line I, the relay L was operated over the r'ollowingcircuit: ground 66 battery Z winding 67- conductor 68--over the talking strands of the cord-conductors otthe calling line-the substation set at A and the switching means J-Pback through the coil 69 of relay L and to battery Z over the conductor 70. This relay attracted the armatures 71 and 72 for purposes to be described. The insertion of the plug P, into the jack J completed a circuit through the relays F, and Q as follows: ground 75F 65--62767173-77 Q -batteryZ to ground 78. The relay F, cuts off the line relay D, and lamp E, and the relay attracts the armatures 49 and 52 and disconnects the operators'set from the cord circuit; a Y

Assuming that the signal 80 at the station E responds to the character of current produced by the generator U, the keys R and S are depressed, closing the switches81-82 and Sit-84. These keys lock down. A circuit is completed through the relay T as follows: ground 85-battery Z, -,switch 8687T--conductor 88-switch 89-90 conductor 91-'8483-ground at 92. The

contact 60,sleeve contact 61,1and ring conrelay T thus energized, attracts its armature 93, breaking the sleeve strand of the cord at 93-94 and closing a switch, 93-95 in the ringing circuit. The relay T attracts its and completingan alternate circuit for the relay Q toinsure its operation during the ringing. This circuit is traced as follows: 78-Z -Q 77 conductor 2-99-100- 88-89-90-91-84-83-92. The ringing now begins and continues at intervals determined by the commutator 101. The ringing circuit is traced as followes: during the ringing period from the ground 102- through U and the commutator 101 and during the silent period from the ground 103 to the commutator 101--in both cases to the spring m l-through the switch 81-82- conductor 105 -relay V, which will not be actuated until the subscriber responds-98- 96-60-63-6-80-7-64-451-93-95-resistance 110-Z,,-85. When the subscriber responds, the switch hook 111. will rise and engage the contact 112, substituting for the bell bridge a low resistance bridge, including the talking set. The flow. of current over the circuit described, including the: talking set at B, will now be sufficient to operate the relay V, which will attract its armature 8? and interrupt the circuit of the relay T at 86-87, restoring the switches controlled by the relay T to the position illustrated'in Fig. 1, thereby restoring the cord circuit, taking off the ringing machine and restoring the circuit of relay (1} through cut-' of? relay F 7 When the subscriber responded, the relay W was also actuated over the conductors 113 11e u1e strands 1 and 3 of the cord circuit and the line conductors 6 and 7.

This relay attracted its armature 90, further interrupting the circuit of the relay T at 89-90. Conversation now takes place with the operator excluded, andv at the completion of the conversation, the subscribers hang up their receivers, whereupon the relays L and TV will be de-energized. The deenergiza-.

tion of the relay L completes a circuit-of the relay X; as follows: ground 120-battery Z -relay X-conductor ,121-contacts 74-7'1-conductor 76-62-65 -F -ground 75. The relay X- attracts its armatures 130 and 131, interrupting the cord circuitat 130-132and 131-133. The attraction of.

the armature 36 interruptsthe circuit of the relays H and F at 86-87, restoring these relays and the switch controlled thereby to normal. The attraction of the armature 140.

closesa switch 140-1411 and completes a circuit through the lamp Y, as follows": 142-. -14:014l-l4 3-1 l4l-40'--battely Z -tO i150-batte'ry ground at 39., The illumination of the lamp Y indicates to the operator that the subscribers are through, so that she pulls out the plugs and restores the system to normal.

By the operation of the relay X and the d'ssconnection oi the plug from the cord, the line at I is immediately released and its line signal restored to normal, so that the subscriber can at once send in a recall, which can be answered by the operator controlling the cord C, or the operator at another position. This line is also released for incoming calls during the period elapsing between the termination of the conversation and the withdrawal of the plugP from the jack J.

Assuming that in answer to the initial call ofthe subscriberat A some other operator plugged into a'multiple jack of the line I before the operator controlling the cord C did so, in that case the shunt 13 at the other cord circuit: will have been completed, so that all of the current will flow through this shunt and comparatively none through therelay H in the cord the presence of the resistance K therein. The relay L, however, will be actuated, completing a special tone circuit through the operators set at G, as follows: ground Z,-operators set at (Er-48- 48-44-160-72-16l-condenser 162-interrupter O-to'ground at 163. This signal will indicate to the operator that she i'stoo late, as the call has already been answered, whereupon she withdraws the jack J. A yisible'signal. will givento the operator, as a circuit completed for the relay M from also be will be the circuit of the lamp N, which will be energized. Observing either of these signals, the operator will withdraw the plug P from the jack J, allowing the otheroperator to complete the call without interference.

In, the form shown in Fig. 2 a relay K is employed in place otthe resistance K illustrated in Fig. 1. If the operator controlling the cord circuit C, inserts the plug P into the jack J, subsequentto the connection of someother cord to the line I, the currentthrough the circuit including the relay K, will be insufiicient to operate the relay H,. but sufficient to operate the relay,-

K,, which will attract an armature 200 and close a switch 200-201, completinga circuit through the relay (6 as follows: ground 202 a conductor 203-201-200-204- 205-206-now closed cont-acts 207-208- the jack J', The relay (5 will attract its circuit C, owing to her plug P from ground 16d M 161 72 -16()-44l-43 -48t0 ground at 150.. The relay M will attract its armature 170, closing a switch 170-171 in armature 210 .closing a switch 210-211 in at the conductors 32 i and first to be inserted armature v 341, which will indicate to the opera circuit which includes a special tone device 0, and the operators set G The relay a,

will also attract the armature 212, closing a cation shown in Fig. 3, I will give a brief description of the operation. In order to complete a connection, the subscriber at A, removes the receiver 307 from the hook switch 308, which completes circuit through the line relay 1),, andcauses the operation of the line lamp E whereupon the operator at the station III, controlling the cord C will insert the plug P into the jack J all of which will be understood from previous descriptions. A circuit will be completed through the cut-off relay F, and the high resistance winding 304: of the relay H as follows, assuming that the plug P is the v 7 into a jack of the lineI to answer this aarticular call:

H, will be energized, attracting its armature 3l5and completing a shunt 316 about the 1 high resistance winding 30%. This shunt includes the low resistance w nding 305, so

that the relay will be maintained energized.

If a second operator now inserts the plug of another cord into a multiple jack of the line A such as a plug P, of the cord circuit C,

into jack J the relay H which corresponds to the relay H will not be operated because the high resistance winding 320 thereof will be shunted b'vflthe low resistance winding 305 of H The relay H will also attractv armatures 321, 322 and 323, connecting the operators set G, to the cord circuit-through the conductors 32 i and 325.

When the plug P was inserted into the jack J the relay L was operated over the cord and line circuit, whereupon the armature 330 will be attracted, openlng a swltch 330 331 in the circuit of the relay X5 and" lamp t relay 7 will also be energized over a circuit from ground at 335.the windings ot'relay L .,-the portions of the cord 325 and back to ground at 336. This relay will attract an I 3&0 and cause the lighting of the lamp tor that she is the first to plug into a' jack of "the line 1,. If, however, some other operatorhas preceded her, the relay H not be.-

g V ground at SOS- F 3l(l-3ll3(ll300'312 313 battery Z -ground 314. The relay ing energized, the circuit of the relay f will never be completed and the lamp 341 will never be lighted. 'Having learned-that it is the subscriber at B that is wanted, the operator tests the line through the contacts 3&2

and 343. Assuming that the line 11 is idle,

the plug P is inserted into the jack J completing a circuit through the relay 6 and the called line cut-oil relay F The relay 0 will interrupt the test circuit and cut the operator oil from the cord circuit and will also" relay V The locking circuit 370 of the relay T will be interrupted and the talking connections will be completed. At the't-ermination of the conversation, the subscribers restore the substation sets to the condition shown in the drawing, which interrupts the circuit of the relay L thereby causing the completion of the circuit of the relay. X and lamp Y at the switch 330-331. The relay X will interrupt the strands of the cord circuit and the circuit of the cutoff relay ll, and relay H An alternative circuit for the relay H, was, however, made before the circuit through the contacts 300 and 301 was interrupted. -This circuit is as follows:

ground at 31LZ, low resistance winding 305-conductor 5302303376378 333-379.350351't0 ground at 380. The illumination of the lamp Y gives the disconnect signal and the operator withdraws the plugs, interruptingthe circuit of the relay 6, which will let go the armature 351 and interrupt the circuit of the lowresistance winding 305 of the relay H whereupon-the apparatus will be restored to normal.

Likewise a brief description of theoperation of the embodiment shown in Fig. 4 will apparently be sufiicient to describe the purposes of the apparatus. When the plug P is inserted, a circuit will be completed for the high resistance winding 40 of the relay H, from the'contact 405-through the switch 406407 of the relay X conductor 408- winding 404battery 409-to ground 410. The relay will attract an armature 11, closing a switch 411 412 in the circuit of the relay X It willialso attract its armatures 4:13 and 41 i, closing switches ties-4 15 and 414.-4:16'.and connect the operators set to the cord circuit. It will also attract an armaputs on the the plug of a second cord is inserted into the multiple jack of the line to which the cord C is connected the high resistance winding 404 thereof will be shunted by the low re sistance winding 420 of the cord At the time the plug P was inserted, the relay L was operated, opening a switch 425-426 in the circuit of the relay The plug P is theninserted, energizing the relay 430 which disconnects the operators setfrom the cord, closes contacts in the circuit of the relay X opens up the test circuit L31 and closes contacts in the cord. The operator then depresses the ringing key which energizes the relay T and connects the ringing machine onto the cord circuit. At the response of the called subscriber, the relay V will be energized and the ringing apparatus disconnected from the cord. IVhen the calling subscriber hangs up, the relay L will be de-energized and the circuit oi the relay X will be completed. Likewise the lamp Y will be lighted. The relay X will disconnect the plug P, from the cord and will interrupt the circuit of the winding 420 ofthe relay H at 4:06407. This interruption, however, will not occur until after the closing of a switch 4 40-4A@1 by the attraction of the armature 441 by the relay This will complete a second circuit for the winding 4:20 over the conductor HQ-switch 444-445-to ground 446. When the plug P is withdrawn this circuit will be interrupted at 444-4t45and in turn the circuit of the relay X will be interrupted, so that the system will be restored to normal.

Fig. 5 -illustrates a form of relay which may be employed to cause a make contact before a break. When the winding 500 is enenergized, the armature- 501 is attracted towards the end of the core 502. This armature will rotate upon the edge of the return piece 504 and elevate the spring 506 which carries the contact 803. The'contact' 803 will engage the contact 302 and asubsequent movement of the armature will elevate the spring 507 and break the contacts 300, 301.

From the above description of the embodiments of my invention it will be'apparent that my ideas may be incorporated in a number of different formsof apparatus, some of which I have illustrated simply for the purpose of describing the inventiomand not that I desire to be limited to the form and details thereof, from which many departures may be made without departing from the s irit of the invention. It will also be seen t at my invention contemplates'novel features of construction and combinations and arrangements of the several pa'rtsof the improved s'ystem, whereby certain important advantages are attained by simple, inexpensive apparatus which. performs the desired functions, greatly speeding up the operation of a telephone system. j

I claim:

1. In a telephone system, the combination of a main station, a plurality of telephone lilies, one of which at least terminates at the main station in a plurality of terminals, a plurality of line connect ng means at the its associate relay, each relay when energized connecting its associate set to its associate connecting means and completin its associate shunt about the other similar relays and preventing the energization of the same. 1

2. In a telephone system, the combination of a main station, a telephone line terminat ing at the main station in a plurality of terminals, a pluralityof cord circuits, switching means to connect each cord circuit ,to a

line terminal, an operators set associatedwith each cord circuit, a plurality of similar relays, one of which is associated with each cord circuit, each relay controlling the connection of its associate operators set with the cord circuit, a resistance connected with each relay and a shunt about each resistance controlled by the relay, means to connect saidrelays in parallel branches of a circuit, all of said relays except one being inoperative when one of saidshunts has been com- I pleted."

3. Ina telephone system, the combination of amain station, a telephone line terminating at the mainstation in a plurality of terminals, a plurality of. cord circuits, switching means to connect the answering end of each cord circuit to a line terminal, an operators set associated with each cord tive when one of said shunts has beencompleted.

4, In a telephone system, the combination 7 1 15 circuit, a plurality of similar devices, one ofv of a main station, a telephone line terminating at the main. station in a plurality of terminals, a plurality of cords atthe main station, switching mechanism including a plurality of line terminal contacts and a plu rality of cord terminal contacts, an operators set associated with each cord, means to connect the answering end of each cord to a line terminal, and means controlled through a plurality of line terminal contacts to give a distinctive signal to an operator undertaking to connect the answering end or a cord with a line to which anothercord is already connected.

5. In a telephone system, the combination of a main station, a plurality of telephone lines leading to the main station and terminating thereat in a plurality of terminals, a plurality of cord circuits at the main station each provided with an answering terminal, means to connect each cord circuit through its answering terminal to a line'terminal, an ope 'atorsset associated with each cord circuit, means to connect said operators set to the cord circuit and means controlled by substation apparatus to prevent the connection of an operators set to a cord circuit and to give the operator a distinctive signal when she undertakesto connect her cord through its answering terminal with a line to which a cord circuit is alreadycolr nected. i

6. .In a telephone system, the combination of a telephone line having a plurality of terminals, a main station at which said tB1II1lnals are located, a plurality of cord circuits at the main station, means to connect each cord circuit to a terminal of said telephone line, an operators set associated with each cord circuit, means to connect the ope 'ators set to the cord circuit, a distinctive visible signal, a distinctive audible signal and meansv operating to give said operator said signals and prevent the connection of her set to the cord when she undertakes to connect said cord toa telephone line to which, a cord has already been connected.

7. In a telephone system, the combination of a main station, a telephone line terminating' at the main. station in a plurality of ter' minals, a plurality of sets of link conductors for connecting telephone lines together, switching means to connect each set of link conductors to a line terminal, an operators set associated with each set of link conductors, a plurality of similar devices, one. of which is associated with each set of linkconductors; each device controlling the connection of an operators set with one of said sets of link conductors, a resistance connected with each device and means about each resistance controlled by a device andapparatusto I connect said devicesin parallel branches of a circuit, all of said devices e2;

ling the connection ofthe operators sets to the cord circuits, circuits for said relays including resistance devices and shunts of said resistance devices controlled by sail relays.

9. In a telephone system, the combination of a main station, a telephone line terminating at the main station in a plurality of ter minals, a pluralityof cord circuits at the main station, an operators set for each cord circuit, relays in the cord circuits controlling the connection of the operators sets to the cord circuits, circuits for said relays includmg resistance devices and normally open shunts of said resistance devices controlled by said relays. i I v 10. In a telephone system, the combination of a plurality of cord circuits, aplurality of operators sets, means to connect said sets to said cords including a plurality of relays, onefor each set and cord, circuits j for said relays, resistance devices independ-- ent of the relays, onerin each circuit anda.

shunt of each resistance device controlled by the relay associated therewith.

1.1. In a telephone system, a plurality of sets of link conductors, an operators set for each set of link conductors, aplurality of relays in multiple circuit, each relay controlling the connection of an operators setto a set of link conductors, a resistance device independent of the relay in series with eaclrrelay and a shunt of each resistance device controlled by the relay associated therewith. i 1

12. In a telephonesystem, the combination'of a plurality of cord circuits, a plurality of operators sets, one associated with each cord, at sleeve relay in each cord controlling the connection of the associate. operators set with the cord. means to connect said relays in multiple circuit,,including a? plurality ofbranches, a resistance device in each branch in series with one of said relays, and a shunt of eachresistance device controlled by the relay associated therewith.

r 13. In a telephone'system, the combination of a telephone line terminating at1a main station ina, plurality -of'terminals,a

plurality of cord circuits at the main sta-- tion, an operators set associated with each cord, adapted to be connected to the talking strands ofthe cords, a relay associated with eachcord controlling the connectionof each" setto its associate cordja'magnetin the ci-rcuit of each. of said relays, a shunt of each of said magnets controlled by such of said relays as is associated therewith and a distinctive signalling device controlled by one of said magnets for informing an operator when she has connected a cord associated with her set to a calling line to which another cord is connected 14:. In a telephonesystem, the combination of a plurality of sets of link conductors, an operators set for each set of link conductors, each link conductor being provided with talking strands, a plurality of relays, (one associated with each link conductor), in multiple circuit, a circuit for each relay including a portion of a talking strand of its associate link conductors, each relay controlling the connection of an-operators set to a set of link conductors, a resistance device independent of the relay in series with each relay and a shunt of each resistance device controlled by the relay associated therewith.

.15. In a telephone system, the combination of a main station, a plurality ofitelephone lines leading to the main station and terminating thereat in a plurality of terminals, a plurality of cord circuits at the main station, each provided with an answering terminal including a ring contact, means to connect each cord circuit through its answering terminal to a line terminal, said means including a ring contact, an operators set and means controlled through said ring contacts to give a distinctive signal to an operator undertaking to connect the answering ends of a cord with a line to which another cord is already connected.

16. In a telephone system, the combination of a main station, a telephone line terminating at the main station in a plurality of line terminals, a plurality of cords at the main station, an operators set associated with each cord, means to connect the answering end of each cord to a line terminal and means to give a distinctive signal to an operator undertaking to completely connect the answering end of a cord with a line to which another cord is already connected.

17. In a telephonesystem, the combination of a main station, a telephone line terminating at the main station in a plurality of terminals, a plurality of cords at the main station, an operators set associated with each cord, means to connect the answering end of each cord toa line terminal and means controlled by a telephone subscriber to give a distinctive signal to an operator undertaking to connect the answering end of the cord with a line to which another cord already connected.

18. In a telephone system, the combination of a'main station, a plurality of telephone lines leading to the main station and terminating thereat in a plurality of terminals, a plurality of link conductors at the main station, each provided with an answering terminal, means to connect each link conductor through its answering terminal to a line terminal, a supervisory relay in the link conductor, an operators set associated with each cord circuit, means to connect said 01)- erators set to a cord circuit and means ineluding said supervisory relay to prevent the connection of an operators set to a cord nection of two of said sets to said line and apparatus controlled through a sleeve contact to give a distinctive signal to an operator undertaking to connect her set to said line while another operators set is connected thereto.

20. In a telephone system, the combination of a telephone line having a plurality of terminals, a plurality of cord circuits, each provided with a plug adapted to co-operate with said line terminals, each cord having a tip and a second contact to the rear thereof, an operators set for each cord, means to prevent the contemporaneous connection of two operators sets to the same line and apparatus controlled through a second contact of a plug to the rear of the tip contact for giving a distinctive signal to an operator attempting to connect her cord to a line to which a cord is already connected.

21. In a telephone system, the combination of a calling telephone line, a sub-station telephone set thereon, a main station, a telephone switchboard at the main station comprising a plurality of operators positions, an operators telephone set for each position, means under the control of an operator to connecther set to the calling telephone line, means to disable the line connecting means of all except one of said operators positions attempting to make connection with the said calling line, and visual signal apparatus con trolled thereby to transmit a distinctive signal to the unsuccessful operators positions.

' 22. In a telephone system, the combination of a calling telephone line, a substation telephone set thereon, a main station, a telephone switchboard at the main station comprising a plurality of operators positions, an operators telephone set for each position, means under the control of an operator to connect her set to the calling telephone line, means to disable the line connecting means of all except one of said operators positions attempting to make connection with the said calling line, apparatus controlled thereby to transmit a distinctive signal to the unsuccessful operators positions, and a plurality In witness whereof, I have signed my of signals different in character at each open name in the resence of two witnesses this 10 ators position and adapted to be operated 12th day of ctober, 1914:. a under the control of said apparatusfwhenii f said line connecting means of the operators FRANK SLOUGH' position is made inoperativeby apparatus Witnesses: I of a previously connected operatorsposition F. O. RIGHEY, line connecting means. GEO. E. ROBERTS. 

